Anchorages of rod shaped tie members of prestressed concrete



Feb- 7, 19 u. FINSTERWALDER 2,970,406

ANCHORAGES OF ROD SHAPED TIE MEMBERS OF PRESTRESSED CONCRETE Filed June15, 1955 2 Sheets-Sheet 1 FIG. 1 FIG. 3

FIG. 4

u. FINSTERWALDER 2,970,406

Feb. 7, 1961 ANCHORAGES OF ROD SHAPED TIE MEMBERS OF PRESTRESSEDCONCRETE Filed June 15, 1955 2 Sheets-Sheet 2 FIG. 6

AN CHORAGES OF ROD SHAPED TIE MEMBERS OF PRESTRES SED CONCRETE UlrichFinsterwalder, Munich, Germany, assign'or to Dyckerhotf & WidmannKommanditgesellschaft, Muchen, Germany Filed June 15, 1955, Ser. No.515,699

2 Claims. (Cl. 50-128) The present invention relates to the anchoring ofrod shaped tie members in prestressed concrete into which high tensileforces are introduced either before the hardening of the concrete in atension bed or after the hardening of the concrete.

The primary object of the present invention is to achieve an efiicientanchorage of high initial tension loads with the aid of simple means andat a low cost.

The invention consists in the provision of one or more locking membersprojecting annularly over the surface of the tie rod and approximatelyof triangular cross section, in conjunction with a reinforcementenclosing the locking member or members.

By the cooperation of the locking members transmitting the anchoringforce to the concrete with a reinforcement which surrounds the rod inthe anchoring area and which prevent the radial splitting up of theconcrete body in planes passing through the axis of the rod, anexcellent transmission of the entire forces is ensured.

A particularly simple construction of the anchorage according to thepresent invention may be achieved by using a thread rolled on in a coldrolling process, which thread may be regarded as a plurality of lockingmembers arranged in series. It is known that a rolled on thread has agreater diameter than the shaft in the region of the thread, in contrastto an incised thread. To achieve extraction of a rod embedded inconcrete, and provided with a rolled on thread, the hole would have tobe enlarged to the greater thread diameter or the concrete would have tosplit radially owing to the anchorage. Since this is prevented by acorrectly calculated'and arranged reinforcement, a surprisingly powerfulforce is required to extract a tie rod of the present invention from theconcrete.

In the preferredform of the new anchorage locking members are used whichare of approximately triangular cross section and project annularlybeyond the surface of the tie rod.

The fixing of the locking members on the tie rod is carried outaccording to the invention not exclusively with a form-dependentconnection, but in a combination of form-dependent connection andfriction lock. For this purpose each locking member may be provided withan inner thread by which it is screwed onto the end of the 'tie rod tobe anchored. Another possibility of obtaining a form-dependentconnection consists in the feature that the locking member is so pressedinto the serration of a thread on the rod, under the action of radialforce components, by hammer blows for example, that a provisional seatfor the locking member on the tie rod is ensured. The locking member mayalso be shrunk onto the tie rod or secured thereto by any other suitablemeans.

When introducing the initial tension load into the tie rod, thereinforcement enclosing the locking member causes a pressure on thelocking member on all sides, radially directed towards the axis of thetie rod, whereby the friction lock is produced. At the same time theatent F 2,970,406 Patented Feb. 7, 1961 outer surface of the lockingmember may be so constructed that it favours the occurrence of the saideffect, namely the production of a friction lock. By selecting asuitable bevel or incline of the outer surfaces, the radial pressuresoccurring may be laterally directed towards the axis of the rod wherebythe locking member is suitably keyed.

It is preferable to proportion the locking member always so. that itreduces its diameter by shrinkage under the action of the radial forceswhereby these forces become effective as friction forces. To assist thiseffect it is preferable to slit the locking member radially in order tocut out the annular effect, since this would reduce the frictionpressure.

The concrete is pressure stressed round about the locking member in aradial and a tangential direction, that is to say in two directionsextending at a right angle to each other. According to experience thestrength of the concrete is particularly high under such high stressing.It reaches a multiple of the crushing strength of cubic proportion sothat such a locking member may be constructed much smaller than a normalanchor plate.

The reinforcement enclosing each locking member may consist of a spiralwhich may be fixed in the desired position relative to the tie rod. Forthis purpose the ends of the spiral may engage around the tie rod with afriction lock effect for example the locking member and the appropriatespiral may also be interconnected by intermediate members. 7

Instead of a spiral a conical ring may also be used as a reinforcingmember corresponding in diameter approximately to the said spiral andwhich points towards the end of the tie rod with the smaller opening andcan be firmly connected by cross-pieces to the locking member. Lockingmember cross-pieces and anchoring ring may also consist of one piece.

As a further construction of the invention the locking member may in ananchorage having only one locking member screwed onto the end of the tierod, be supported against the inner wall of a funnel shaped tensioningcup, slipped over the enclosing tube of the tie rod and have a hexagonalhead towards the end of the tie rod.

Transverse tensions at the anchorage point of the tie rod may be avoidedin accordance with the present invention in an anchorage having only onelocking member screwed onto the end of the tie rod by the feature thatthe locking member is supported against an annular bowl slipped over thetie rod. In this. case the forces radiating from the locking member aresupported against the edge of the said bowl and result in annularvtensile stresses which are completely received by the bowl. At the sametime the forces radiating from the locking member are reversed in themarginal area of the bowl. By this means the transverse tensile stressesare kept low.

In a preferred form of construction of this embodiment of the anchorageof the bowl which is particularly important to the art the edge of thebowl disposed on the tie rod is raised parallel to the axis of the tierod, while the outer edge of the bowl is curved with a radiuscorresponding approximately to the diameter of the tie rod. In a furtherconstruction of the object of the present invention holes may bearranged in the bottom of the annular bowl in order to prevent theformation of air cushions inside the bowl during the concreting.

The locking member may be provided on the tension side of the steel rodwith a hexagonal head so that it can be tightened by mounting a socketwrench after the tension loads have been introduced into the tie rod inorder to anchor the induced tensile forces.

Further features of the present invention and details of the advantagesobtained thereby will be apparent from 9 during the pressing out withcement mixture.

the following description of various forms of construction of theanchorage shown in the accompanying draw Figures and 6 show inlongitudinal section and plan view an anchorage with a locking memberand a conical ring connected thereto by yokes or cross pieces.

Figure 7 is a longitudinal section through an anchorage having atensioning cup shaped member and a weldedon spiral reinforcement.

In Figures 1-4 of the drawings the anchorage of a rod shaped tie member1 is shown in concrete on the pure anchoring side, that is to say theside on which the end of the tie rod is firmly anchored, .it beingassumed that the tension loads are exerted on the tie rod from the otherend thereof.

A locking member 3 annularly projecting beyond the surface of the tierod, and approximately of triangular cross section, is screwed onto thethreaded end of the tie rod 1 which consists of high grade steel. Thethread 2 may be rolled on by cold rolling or incised. The side surfacesof the locking member of triangular cross section are inclined towardsthe axis of the tie rod by about 30 to 60 but preferably 45. The tensileforce introduced into the tie rod 1 is radiated to the sides by thelocking member 3 and in a simple manner transmitted over a lengthystretch of the concrete.

In order to prevent radial splitting up of the concrete owing to thelateral forces exerted by the locking member, the latter is enclosed bya spiral reinforcement 4. In the embodiment shown in Figures 1 and 2 theupper and lower windings 5, 6 of the spiral are guided around the tierod 1 in a friction lock to prevent changes of position of the spiraland the locking member relative to each other.

In the embodiment shown in Figures 3 and 4, the spiral 4 and the lockingmember 3 are interconnected by angle members 7 to maintain theirrelative position. A

rope, 8 is used to produce ventilation of the jacket tube. 1

The end of the jacket tube 9 is sealed against the tie rod 1 by means ofa sleeve 10.

Figures 5 and 6 show the anchorage of a tie rod at the end of the rodbedded in the concrete. The tie rod 1 in this form of construction isalso provided with a thread on which the locking member 3 is screwed. Inthis form ofconstruction shown in Figures 5 and 6 the spiralreinforcement of Figures 1-4 is replaced by a conical ring 11 which isfirmly connected to the locking member 3 by yokes or cross pieces 12.The latter may be secured by welding to the locking member 3 and to thering 11. They may however be formed integrally with the locking memberand the ring.

In the longitudinal section through the stressed end of a tie rodofFigure 7, the end of the tie rod 1 is again provided with a thread on towhich a locking member 3 is screwed. The outer part of the lockingmember 3 is constructed as a hexagon 13 and is used for subsequently 4mounting a socket wrench such as a box spanner for tightening thelocking member, that is to say, for anchoring the tensile forcesimparted to the tie rod.

The locking member 3 is supported against the inner wall of afunnel-shaped tension cup 14 which is slipped onto the end of a tubularjacket 9 receiving the tie rod 1. The tension cup 14 is supportedagainst a bead 15 in the jacket 9. To prevent soiling and blocking ofthe inner space 16 of the tension cup during the concreting operation,the tension cup is closed by a plate 17 on which is welded a nut 18 forscrewing the plate onto the thread of the tie rod. In addition, a'spiral reinforcement 19 for receiving transverse tensile stresses, iswelded to the tension cup 14. The rope 8 is used to produce aventilation of the jacket 9 during the subsequent filling with cementmixture. The point where the rope 8, which forms the ventilationpassage, is introduced into the jacket 9, is sealed by a sleeve 20.

I claim:

1. In a prestressed concrete structure, an anchoring tie rodconstruction comprising, in combination, an elongated stressable tie rodmember of steel having threads adjacent one end, an annular lockingmember engaging the threaded end of said rod over a large cylindricalarea along the threaded surface of said rod and having the shape of twofrusto-cones integrally connected at their bases and having incross-section at each side a triangular confine with the vertex of thetriangle approximately midway between the terminal surfaces of saidlocking member, the sides converging at said vertex forming an angle ofbetween 30 and 60 with respect to the axis of said tie rod member, theshape of said annular locking member transmitting stress forces fromsaid tie rod member radially outwardly and a spiral reinforcing membersurrounding said tie rod member for receiving transverse tensilestrength stresses in saidconcrete after hardening, and frictionallocking means formed at both end portions of said spiral member near oneend of said rod to prevent at said one end displacement of said spiralmember relative to said rod, the remaining portion of said spiral memberbeing unattached to said rod.

2. A'prestressed concrete structure incorporating an anchoring tie rodconstruction as claimed in claim 1 wherein the angle defined by theconical surfaces meeting at the vertex of said triangular cross-sectionof said annular locking member is substantially 45 with respect to theaxis of said rod.

References Cited in the file of this patent UNITED STATES PATENTS903,909 Steiner Nov. 17, 1908 1,967,391 Blackburn July 24, 19342,137,718 Friberg Nov. 22,1938 2,695,754 Karig Nov. 30, 1954 FOREIGNPATENTS 612,324 Great Britain Nov. 11, 1948 660,438 Great Britain Nov.7, 1951 839,026 Germany May 15, 1952 1,011,997 France Apr. 9, 19521,019,520 France Oct. 29, 1952

